1. Field of the Invention
The present invention generally relates to an organic light emitting display (OLED) pixel structure and a method for manufacturing the same and, more particularly, to an OLED pixel structure and a method for manufacturing the OLED pixel structure using a novel pixel arrangement so as to improve the resolution of an OLED panel.
2. Description of the Prior Art
In OLED manufacturing, full color displays implemented using red (R), green (G) and blue (B) organic electro-luminescent (EL) materials exhibit high brightness, high contrast, high color saturation but suffer from limited resolution because the opening areas on the shadow mask for EL material evaporation can not be effectively reduced.
Please refer to FIG. 1, which is a schematic diagram showing an evaporation process for an organic EL material. In mass production, the current EL evaporation process uses a single EL source in a vacuum chamber. As shown in FIG. 1, a shadow mask 10 is disposed between a substrate 12 and an EL source 14, wherein the surface of the substrate 12 to be deposited thereon faces downwards to the EL source 14. When the EL source 14 is heated up, the organic EL material is evaporated through a plurality of openings 102 in the shadow mask 10 onto a plurality of deposited regions 122 on the substrate 12. By shifting the shadow mask 10 and the substrate 12, the EL source 14 evaporates the organic EL material for one of the three colors onto the pre-determined deposited regions 122 and then evaporates the organic EL materials for each of the other two colors. Finally, the organic EL materials for R, G and B are formed on the deposited regions 122 on the substrate 12, wherein each of the deposited regions 122 corresponds to a sub-pixel.
Please refer to FIG. 2, which is a schematic circuit diagram showing equivalent pixel circuits and driver circuits of an OLED panel. The OLED panel 20, using two thin-film transistors (TFT's) for example, comprises data lines D1, D2, . . . , Dm and scanning lines G1, G2, . . . , Gn. Each data line and an intersecting scanning line are used to control a display unit 21. For example, a switching transistor TS11 comprises the gate coupled to a scanning line G1 and the source coupled to a data line D1 for storage and addressing of an image data. A driving transistor TD11 comprises the gate coupled to the drain of the TS11 and the source coupled to a voltage source VDD for controlling the driving current according to the storage capacitor CS11. One end of the storage capacitor CS11 is coupled to the drain of the TS11 while the other end is coupled to a reference voltage VL. The anode of the OLED is coupled the drain of the TD11 and the cathode is coupled to the ground GND.
The schematic circuit diagram of FIG. 2 comprises the switching transistors TS11˜TS1m, TS21˜TS2m, . . . , TSn1˜TSnm, the driving transistors TD11˜TD1m, TD21˜TD2m, . . . , TDn1˜TDnm, the storage capacitors CS11˜CS1m, CS21˜CS2m, . . . , CSn1˜CSnm, and the OLED's. Each display unit 21 corresponds to a sub-pixel. A pixel comprises three sub-pixels for R, G and B corresponding to three display units. In other words, in FIG. 1, when the organic EL material is evaporated through the plurality of openings 102 in the shadow mask 10 onto the plurality of deposited regions 122 on the substrate 12, the area of one of the openings 102 corresponds to the area of a sub-pixel. Each sub-pixel corresponds to two TFT's and one storage capacitor.
Please refer to FIG. 3A and FIG. 3B, which are schematic diagrams showing pixel arrangements of an OLED panel. In FIG. 3A, there are a plurality of pixels 31 comprising a red sub-pixel 312, a green sub-pixel 314 and a blue sub-pixel 316 on an OLED panel 30. Each sub-pixel corresponds to two TFT's and one storage capacitor as shown in FIG. 2. Moreover, sub-pixels with different colors have different life-times. The sub-pixel with the shortest life-time limits the durability of whole display panel. If the red sub-pixel and the blue sub-pixel, which exhibit lower brightness, are designed to have larger areas, the driving currents for the red sub-pixel and the blue sub-pixel could be lowered so as to enhance the durability of whole display panel. In FIG. 3B, there is a white (W) sub-pixel 368 in addition to a red sub-pixel 362, a green sub-pixel 364 and a blue sub-pixel 366 in each of the pixels 36 on the OLED panel 35. The red sub-pixel 362, the green sub-pixel 364, the blue sub-pixel 366 and the white sub-pixel 368 may have different areas. Since each of the sub-pixels corresponds to two TFT's and one storage capacitor as shown in FIG. 2 and the area of each of the sub-pixels is determined by the opening 102 of the shadow mask 10. In other words, the sub-pixel area formed by evaporating an organic EL material through the opening 102 of the shadow mask 10 onto the deposited region 122 can not be unlimitedly reduced. Therefore, the resolution of the OLED panel is limited by the evaporation process.
Therefore, there exists a need in providing an OLED pixel structure and a method for manufacturing the OLED pixel structure using a novel pixel arrangement so as to improve the resolution of an OLED panel.